Current monitor for threshold detection

ABSTRACT

A device for monitoring the current supplied to a missile and its firing mechanism which gives a GO-NO-GO indication during flight line checkout and thereby an alert to any existing malfunctions. A Schmitt trigger fires a monostable multivibrator which activates a current amplifier to trigger a power transistor with 5.9 ohms of load resistance connected to the emitter thereof. This load resistance simulates the actual missile firing mechanism. The current developed through the load resistance is applied to a current sensor that triggers a driver and relay. If the current is of sufficient magnitude, the relay is energized and a green lamp will illuminate indicating a &#39;&#39;&#39;&#39;GO&#39;&#39;&#39;&#39; condition. If insufficient current is applied to the device, the relay will not energize and a red lamp will illuminate indicating a &#39;&#39;&#39;&#39;NOGO&#39;&#39;&#39;&#39; condition.

United States Patent Gullion [451 Mar. 28, 1972 CURRENT MONITOR FORTHRESHOLD DETECTION [72] Inventor: Billy B. Gullion, Reistertown, Md.

[73] Assignee: The United States of America as represented by theSecretary of the Navy [51] Int. Cl. [58] Field olSearch ..340/253 P,340/410 ..G08b 21/00 340/253, 255 A, 214, 410, 421,

Primary Examiner-John W. Caldwell Assistant ExaminerDaniel MyerAtt0rney-R. S. Sciascia and Thomas 0. Watson, Jr.

[5 7] ABSTRACT A device for monitoring the current supplied to a missileand its firing mechanism which gives a GO-NO-GO indication during flightline checkout and thereby an alert to any existing malfunctions. ASchmitt trigger fires a monostable multivibrator which activates acurrent amplifier to trigger a power transistor with 5.9 ohms of loadresistance connected to the emitter thereof. This load resistancesimulates the actual missile firing mechanism. The current developedthrough the load resistance is applied to a current sensor that triggersa driver and relay. It the current is of sufficient magnitude, the relayis energized and a green lamp will illuminate indicating a 60" 56References Cited l 1 condition. If insufficient current is applied tothe device, the UNITED STATES PATENTS relay will not energize and a redlamp will illuminate indicating a NO-GO condition. 3,281,697 10/1966Hansen et a1. ..325/l51 9 Claims, 3 Drawing Figures INPUT 74 70 H ass ssI, l DELAY I "No so" (TO ALL CIRCUITS) 55 LAMP was" DELAY 54 "so" LAMP(GREEN) (STAGE 2) (STAGE 5) (STAGE 4) (STAGE 5) (STAGE 6) (STAGE 7) T- TSCHMITT MONOSTABLE CURRENT c TRIGGER MULTIVIBRATOR AMR fA T E s E'L s oR k/l/ ER PATENTEDMAR28 I972 13, 653,020

SHEET 2 [1F 2 CURRENT MONITOR FOR THRESHOLD DETECTION STATEMENT OFGOVERNMENT INTEREST The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION The present invention relates generally toimprovements in test circuitry, and more particularly it pertains to anew and improved device for monitoring the current applied to a missileand its firing mechanism.

Those concerned with the development of missile firing circuitry foraircraft have long recognized the need for a reliable and accuratedevice that will checkout and test the circuitry and alert operatingpersonnel to any existing malfunctions in order to prevent sending theaircraft into combat with a faulty missile firing circuit that couldhave disastrous results. Such hazards as moisture in the aircraftwiring, bad solder joints, switch resistance, faulty wiring, etc., cancause an increase in line resistance that will reduce the currentapplied to the missile firing mechanism. If this happens, when themissile fire" switch in the cockpit is energized, the reduced currentwill cause a delay in activating the missile squibb which will result inthe pilot overshooting the target before the missile is released.

For obvious reasons, it is impossible to check the aircraft circuitrywith the actual missile installed. Also, the full current of at least4.0 amperes must be drawn through the circuitry for the actual timeduration or any reduction due to moisture may not be detected.

In thepast, several devices have been employed in order to perform acomprehensive test of aircraft wiring during flight line testing. Onedevice utilized standard test equipment for the Continuity Test. Thisdevice has not been satisfactory as it is impossible to apply thenecessary current to the circuitry to locate any current reduction dueto moisture and cold solder joints. Another device which has been usedis to connect the correct load resistance in place of the missile andits firing mechanism and pass the current through a circuit breaker thatis 200-300 percent overloaded. The time duration of the pulse lengthbefore the breaker trips is monitored on an oscilloscope. The time ofthe pulse length is then correlated with a calibration curve of eachcircuit breaker used. However, this method necessitates transporting anadditional piece of commercial equipment to the flight line thatrequires an AC power source. In addition, each circuit breaker used musthave a separate calibration curve plotted and, after using them for aperiod of time, they cannot be depended upon to trip at the same timeperiod for the exact same current pulse. Therefore this device has alsobeen unsatisfactory.

OBJECTS OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a simple and compact device that is accurate andreliable to checkout and test missile firing circuitry for aircraft.

Another object is to eliminate the need for additional equipment andcalibration curves and to provide a simple GO-NO- GO indication forflight line checkout.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a checkout and test of missile firing circuitry for aircraft.The device to simulate the missile and its firing mechanism is connectedin place of the actual missile and its firing mechanism and iscalibrated to draw 4.0 amperes when 27 volts DC is supplied by thecockpit missile firing switch. The first stage of the invention iscomposed of a delay circuit of approximately milliseconds to allow allother stages to stabilize before circuit activation. The second stage isa Schmitt trigger that fires a monostable multivibrator developing apositive pulse for 50 milliseconds. This stage activates a currentamplifier that triggers a power transistor with 5.9 ohms of loadresistance connected to the emitter thereof. This load simulates theactual missile firing mechanism. The current developed through the loadresistance is applied to a current sensor that triggers a driver andrelay. If the current is of sufiicient magnitude (4.0 amperes), thedriver fires, the relay is energized and a green lamp will illuminateindicating a GO" condition. The driver transistor is biased so that ifthe current is less than 4.0 amperes, the relay will not energize and ared lamp will illuminate indicating a NO GO condition. A final stage iscomposed of a delay circuit which prevents either lamp (GO or NO GO)from illuminating until the cycle is-completed. Overall accuracy iswithin 5 percent. Also, the device of the present invention isequippedwith a probe that connects to the aircraft circuitry at themissile location.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the basic aircraftmissile firing circuitry simplified for analytical purposes.

FIG. 2 illustrates the overall circuitry of the present invention inblock diagram form.

FIG. 3 shows a schematic wiring diagram in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1, which is asimplified circuit to illustrate the principle of the invention, showsthe aircraft power source of 27:2.0 volts DC which is supplied by theactual pulse from the cockpit missile firing switch. The entire cycle tobe described is activated by depressing the missile fire" switch locatedin the cockpit of the aircraft. The switch is momentarily held for 2 to3 seconds, then released. R represents the line resistance that willreduce the current applied to the missile firing mechanism and consistsof such things as moisture in the aircraft wiring, bad solder joints,switch resistance, faulty wiring, etc. RLOAD is the load resistance andsimulates the actual missile firing mechanism. The actual aircraftparameters for this current are:

R 0.43i0.07 ohms.

R 5.91-0.10 ohms.

Time duration= 45 to 50 milliseconds.

The device to simulate the missile and its firing mechanism is shown inthe block diagram of FIG. 2. The input represents the power suppliedwhen the missile firing switch in the cockpit is depressed. The firststage is composed of a delay circuit of approximately 100 millisecondsto allow all other stages to stabilize before circuit activation. Stage2 is a basic Schmitt trigger that fires the one shot multivibrator ofstage 3 developing a positive pulse for 50 milliseconds. The third stageactivates the driver or current amplifier of stage 4 which triggers thecurrent gate of stage 5. Stage 5 is composed of a power transistor with5.9 ohms of load resistance connected to the emitter thereof. This loadresistance Z simulates the actual missile firing mechanism. The currentdeveloped through the load resistance Z (5.9 ohms) is applied to thebiasing network or current sensor of stage 6 which triggers the driverand relay of stage 7. If the current is of sufficient magnitude (4.0amperes), the driver of stage 7 fires, the relay is energized and agreen lamp will illuminate indicating a G0 condition. The drivertransistor of stage 7 is biased so that if the current in stage 5 isless than 4.0 amperes, the relay will not energize and a red lamp willilluminate indicating a NO GO condition. Stage 8 is composed of a delaycircuit that prevents either lamp (GO or NO GO) from illuminating untilthe cycle is completed. Overall accuracy is within 5 percent. Inaddition,

the device is equipped with a probe (not shown) that connects to theaircraft circuitry at the missile location.

Referring to the schematic diagram of FIG. 3, each stage of theinvention will now be described in detail. Stage 1 is composed of a1,000 ohm resistor 10 and a 100 microfarad capacitor 12. This networkdelays the trigger input for 100x10 milliseconds which is necessary toallow the other circuitry to stabilize and to prevent erratic firing ofthe current gate of stage at the moment of turn-on. Stage 2 is a basicSchmitt trigger that develops the firing pulse for stage 3. It iscomposed of transistors 14 and 16 and the necessary components todevelop a positive current pulse which consists of resistors 18, 20, 22,24 and 26, capacitor 28 and a diode 30. Stage 3 is monostable (one shot)multivibrator with an adjustable time delay and is composed oftransistors 32 and 34, resistors 36, 38, 40 and 42, capacitor 44 andZener diode 46. It is calibrated by adjusting resistor 38 for a positiveoutput pulse of 50 milliseconds. Zener diode 46 (18 volts), inconjunction with resistor 42, limits the voltage applied to this stage.This is necessary to prevent the positive current pulse from varying intime duration due to the variation in aircraft voltage. The output ofthis stage fires transistor 48. Stage 4 is a current amplifier whichconsists of transistor 48 that drives transistor 50 into hardconduction. Stage 5 is the current gate that is composed of powertransistor 50 and the necessary load resistor 52 (Z to develop thecurrent pulse of 4 amperes. The maximum current is triggered for a timeduration of 50 milliseconds as stated above. The current developedthrough load resistor 52 is applied to stage 6.

Stage 6 is the current sensor or biasing network for transistor 54 andis composed of resistor 56, capacitor 58, diode 60 and potentiometer 62.Potentiometer 62 is calibrated to fire transistor 54 if the currentpulse developed through load resistor 52 is 4.0 amperes or more inamplitude. If the current pulse is 3.8 amperes, or less, transistor 54will not fire. Diode 60 is added to help compensate for drift in thefiring point of transistor 54 due to temperature change. Stage 7 iscomposed of transistor 54 and relay 64. The firing point of transistor54 is biased as stated above. When transistor 54 fires, relay 64 isenergized and a G0 lamp 66 (green) illuminates. When relay 64 energizes,current is applied through resistor 68 to the base of transistor 54 tomaintain this condition until power is removed from the entirecircuitry. If transistor 54 does not fire, relay 64 remains in thenormal condition and the NO 00" lamp 70 (red) illuminates. Stage 8 iscomposed of a time delay relay 72 with a delay factor of 200:milliseconds. The purpose of this stage is to prevent voltage from beingapplied to the wiper 74 of relay 64 until the cycle is completed. Thisprevents erratic blinking of either lamp 66 or 70.

The basic circuitry described above can also be used to check and testthe eject-jettison circuit in the aircraft. The only changes to thecircuit would be the value of load resistor 52 from 5.9 ohms to 1.9 ohmsand to modify the input connection to mate with the aircraft circuit.

Obviously many other modification and variations of the presentinvention are possible in the light of the above teachings. For example,one modification of the basic design could include a self-containedpower source that would kee the circuitry in the ready condition at alltimes. However, for the present application it is unnecessary as it willprevent impacting the existing configuration. Another possible variationis a thermistor 76 for temperature compensation, which could beconnected to the collector of transistor 54 as shown in F IG. 3.

What is claimed is:

l. A current monitor for threshold detection of a missile and its firingmechanism, which comprises:

means for producing a current pulse;

a current amplifier activated by said current pulse;

a power transistor triggered by said current amplifier;

means connected to said power transistor for simulating the missilefiring mechanism;

a current sensor to detect the current pulse developed through saidsimulation means and fire a transistor at a predetermined currentthreshold;

means for indicating if said current threshold is reached.

2. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 1, wherein a delay network to providecircuit stabilization is connected to said current pulse producingmeans.

3. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 2, wherein said current pulse producingmeans comprises a Schmitt trigger and a monostable multivibrator.

4. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 3, wherein said simulation means comprisesa load resistor connected to the emitter of said power transistor.

5. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 4, wherein a relay is energized when saidtransistor fires at the predetermined current threshold.

6. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 5, wherein said indicating means comprisesa lamp which is illuminated when said current threshold is reached andsaid relay is energized.

7. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 1, wherein said simulation means comprisesa load resistor connected to the emitter of said power transistor.

8. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 7, wherein said load resistor has a valveof 5.9 ohms.

9. A current monitor for threshold detection of a missile and its firingmechanism as recited in claim 8, wherein the current threshold is 4.0amperes.

1. A current monitor for threshold detection of a missile and its firingmechanism, which comprises: means for producing a current pulse; acurrent amplifier activated by said current pulse; a power transistortriggered by said current amplifier; means connected to said powertransistor for simulating the missile firing mechanism; a current sensorto detect the current pulse developed through said simulation means andfire a transistor at a predetermined current threshold; means forindicating if said current threshold is reached.
 2. A current monitorfor threshold detection of a missile and its firing mechanism as recitedin claim 1, wherein a delay network to provide circuit stabilization isconnected to said current pulse producing means.
 3. A current monitorfor threshold detection of a missile and its firing mechanism as recitedin claim 2, wherein said current pulse producing means comprises aSchmitt trigger and a monostable multivibrator.
 4. A current monitor forthreshold detection of a missile and its firing mechanism as recited inclaim 3, wherein said simulation means comprises a load resistorconnected to the emitter of said power transistor.
 5. A current monitorfor threshold detection of a missile and its firing mechanism as recitedin claim 4, wherein a relay is energized when said transistor fires atthe predetermined current threshold.
 6. A current monitor for thresholddetection of a missile and its firing mechanism as recited in claim 5,wherein said indicating means comprises a lamp which is illuminated whensaid current threshold is reached and said relay is energized.
 7. Acurrent monitor for threshold detection of a missile and its firingmechanism as recited in claim 1, wherein said simulation means comprisesa load resistor connected to the emitter of said power transistor.
 8. Acurrent monitor for threshold detection of a missile and its firingmechanism as recited in claim 7, wherein said load resistor has a valveof 5.9 ohms.
 9. A current monitor for threshold detection of a missileand its firing mechanism as recited in claim 8, wherein the currentthreshold is 4.0 amperes.